There's a wonderfully grisly story by WW Jacobs, "The Monkey's Paw", in which an old couple are granted three wishes. What they want most is to see their long-lost son again. The son, however, has just been killed by a piece of heavy machinery in a ghastly factory accident. The climactic moment comes when they hear his mangled corpse sloshing horribly toward their front door, and the old man uses the last of the three wishes to send him back to the grave.

I detect a curious parallel here to my own recent experience. Having devoutly hoped for many years to acquire American citizenship, now that I have it there's a sense that something monstrous attaches to the fulfilment of the wish. That monstrous thing is of course the Bush administration, and becoming an American at this precise moment in history feels not exactly like a poisoned chalice, but it certainly leaves a bittersweet taste in the mouth.

My sentiments towards this country, where I have lived for more than 20 years, have been like those of many immigrants: fascinated, affectionate, grateful, though somehow never easy to articulate without resort to large vague abstractions. Extensive reading in the history of the Revolutionary period, undertaken for the writing of a historical novel, gave me a largely romantic picture of the colonists' struggle: this plucky band of farmers and fishermen challenging the greatest army in the world, with the wilderness landscapes of early America as a backdrop, and the idea of Liberty shimmering at the heart of it all.

I felt in addition a strong sympathy with their robust hatred of kings, but above all an admiration, verging on awe, in fact, at their intellectual audacity. The act of political imagination it took to write first the Declaration of Independence and then the Constitution - the vaunting idealism of those documents, and the eminent efficacy of the republican model they created so as to establish at least the possibility of social equality, and exclude a future in which tyranny could take hold - this is truly heroic stuff.

But it is hard to detect in America's current leaders the spirit of Sam Adams and Tom Paine, Jefferson and Franklin and all the rest who risked the king's rope for the sake of a republican ideal. Senator Robert Byrd of West Virginia is a keeper of the flame. In a speech on the Senate floor in late March, he said he wept for his country. America is mistrusted around the world, he said, its intentions are questioned, it ignores its friends and risks undermining international order by adopting a radical doctrinaire approach to using its awesome military might. He said America's true power lay not in its ability to intimidate, but to inspire.

I am one of those who have been inspired by America, but the way forward now is dark and uncertain in the extreme. The behaviour of this administration, not least its squandering of the immense goodwill and sympathy the world felt toward us in the wake of September 11, provokes intense anxiety. Many of us continue to reject the legitimacy of the Bush election victory, and indeed this is one of the dilemmas facing the large field of contenders for the Democratic nomination jockeying for position.

Do you speak to the many millions of Americans who regard the Bush presidency as illegitimate, distrust his motives in foreign policy, and tremble at what another four years of his neoconservative cabal will do to civil rights, the environment, the domestic economy, the courts, the labour unions, and not least, tolerance of dissent? Or do you emphasise your hawkishness, on the assumption that nobody who isn't strong on defence can be elected president in 2004?

Most of all, I think, at least at this moment, as the dust settles in Baghdad, and hostile eyes are turned toward Syria and Iran and North Korea, we tremble at the implications of the Bush foreign policy. It has its theoretical foundations in the work of Leo Strauss, an obscure professor at the University of Chicago who died in 1973, and whom James Atlas in the New York Times recently described as the political guru of many senior Bush people.

Rejecting the moral relativism of the 1960s, in a book called On Tyranny, Strauss wrote that "to make the world safe for the western democracies, one must make the whole world democratic, each country in itself as well as the society of nations". He asserted "the natural right of the stronger" to prevail, although he did warn of the dangers of foreign occupation: "Even the lowliest men prefer being subjects to men of their own people rather than to any aliens." Whether or not the administration heeds this last caveat, their commitment to Strauss's programme of domination is borne out in the clumsy arrogance of American "diplomacy" in the run-up to the invasion of Iraq.

Reading Melville's "Billy Budd, Sailor" last week, I came across this description of the Napoleonic wars: "...like a flight of harpies [they] rose shrieking from the din and dust of the fallen Bastille". Substitute "twin towers" for the last word in that sentence, and you have what many of us fear is the foreign-policy agenda of this administration.

Melville is on other minds too, at this fraught time. Jason Epstein, in an essay called "Leviathan" in the New York Review of Books (May 1, 2003), suggested that Moby-Dick is prophetic, even if Bush is no Ahab, and Iraq will not sink the USA as the white whale did the Pequod. It is, rather, a thirst for vengeance Epstein recognises in both Ahab and the Bush people, Ahab's zeal resembling the administration's twisted passion to "Americanise the world, as previous empires had once hoped with no less zeal to Romanise, Christianise, Islamicise, Anglicise, Napoleonise, Germanise, and communise it".

Melville saw the America of his era - and symbolised it in the whale-ship Pequod - as a nation bent on self-destruction, as in fact it was, in that it would shortly tear itself apart over the question of slavery. But the Pequod stands for America in a better, higher sense too - an inspirational sense - in that men of disparate races ship out aboard her, not only Ishmael and Queequeg but Daggoo, and Tashtego, and Fedallah the Parsee - men of all colours and religions, "federated along one keel". The ship has been at sea for some time before Ahab actually appears from below decks, and it is only then that Ishmael glimpses the man who will lead the entire crew, himself excepted, to their deaths, having diverted the ship, as Epstein notes, from its proper purpose, the hunting of whales, to his own private purpose, the seeking of vengeance on the whale that "dismasted" him.

In similar fashion did I - and the hundreds of others who became citizens with me - board the good ship America, with no idea what sort of a captain would eventually emerge from below, and it's this that gives my citizenship its distinctively bittersweet flavour. In vain do I assert that I have joined the America of Adams and Jefferson and Franklin and Paine, for I live in an America whose leaders espouse a Manichean vision of a world starkly divided into good folks and bad. And if it is true that the real national treasures of the United States are her documents - the Bill of Rights, the Constitution, the Declaration of Independence - then the Bush people are no less vandals of our heritage than the Iraqis who, after the fall of Baghdad, looted and destroyed the ancient artifacts of Mesopotamia.

I suspect that much of my ambivalence was shared by my fellow citizens-to-be at the immigration centre in Garden City, New York, that warm, clear day in late April. During the oath ceremony - which was resolutely American, in that all those presiding were jovial and informal, and seemed genuinely happy at what they were about - the official at the podium gave a short speech reminding us that henceforth we must be loyal to our new country "through thick and thin".

Was it my imagination, or was he suggesting that this, now, is an extremely thin bit, but if we just hold on, and vote with our consciences, we will have thicker times in future? I certainly plan to cast my vote for regime change in Washington, and look forward enthusiastically to exercising this most valuable right of the American citizen. Will my single, solitary vote matter? It might, if Florida 2000 is anything to go by, as long, that is, as a right-wing Supreme Court does not step in and award the election to its own favoured candidate.

· This is an edited excerpt from the forthcoming issue of Index on Censorship, Rewriting America, to be published on July 17, price £9.50.